1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method for fabricating an LCD incorporating a liquid crystal dispensing method.
2. Discussion of the Related Art
In general, recent developments in the information communication field have increased demand for various types of display devices. In response to this demand, various flat panel displays such as liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed, some of which have been employed as displays in various products.
LCDs have been used most widely as mobile displays while replacing the CRT (Cathode Ray Tube) because of features and advantages including excellent picture quality, light weight, thin profile, and low power consumption. In addition to the mobile type LCDs, such as a display for a notebook computer, LCDs have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in LCD technology, research towards enhancement of LCD picture display quality has been, in some respects, lacking as compared to other components and characteristics of the LCD. Therefore, to use the LCD in various fields as a general display, the key to developing the LCD lies on whether the LCD can implement a high quality picture, such as high resolution, high luminance, and large-sized screen while still maintaining lightweight, thin profile, and low power consumption.
LCDs may be provided with a liquid crystal panel for displaying a picture, and a driving part for applying a driving signal to the liquid crystal panel. The liquid crystal panel has first and second glass substrates bonded together with a gap between the substrates. A liquid crystal layer is formed by injecting liquid crystal between the first and second glass substrates.
On the first glass substrate (a TFT array substrate, for example), there are a plurality of gate lines arranged in a first direction at fixed intervals, a plurality of data lines arranged in a second direction perpendicular to the gate lines at fixed intervals, a plurality of pixel electrodes in respective pixel regions defined by the gate lines and the data lines arranged in a matrix, a plurality of thin film transistors switchable in response to a signal on the gate lines for transmission of a signal on the data line to the pixel electrodes.
The second glass substrate (a color filter substrate) has a black matrix layer for shielding light from areas excluding the pixel regions, R, G, B color filter layer, and a common electrode for implementing a picture.
The foregoing first and second substrates have a gap between them which is maintained by spacers and are bonded to one another by a sealant. The seal has a liquid crystal injection inlet through which the liquid crystal is injected after the two substrates are bonded and sealed.
After the individual liquid crystal display panels are cut, the space between the bonded two substrates of each LCD panel is evacuated and the liquid crystal injection inlet is dipped in a liquid crystal bath, so that the liquid crystal is injected into the space by a capillary tube phenomenon. Once the liquid crystal is injected into the space between the two substrates, the liquid crystal injection inlet is sealed by the sealant.
However, the related art method for fabricating an LCD having liquid crystal injected therein has the following problems. First, the related art method has a poor productivity because the dipping of the liquid crystal injection inlet in a liquid crystal bath while the space between the two substrates are maintained at a vacuum after the unit panels are cut into individual pieces for injection of the liquid crystal takes much time. Second, the liquid crystal injection for a large LCD, in particular, may cause imperfect filling of the liquid crystal in the panel, which may result in a defective panel. Third, the complicated and lengthy fabrication process requires the use of many liquid crystal injection devices, which occupies much space.
Accordingly, a method for fabricating an LCD by using a liquid crystal dropping method has been under research recently. A Japanese laid-open patent publication No. 2000-147528 discloses the following liquid crystal dropping method.
A related art method for fabricating an LCD by using the foregoing liquid crystal dropping method will be explained. FIGS. 1A-1F illustrate steps of a related art method for fabricating an LCD.
Referring to FIG. 1A, UV sealant 1 is coated on a first glass substrate 3 having a thin film transistor array formed thereon to a thickness of approximately 30μm, and liquid crystal 2 is dropped on an interior of the sealant 1, which is the thin film transistor array part. No liquid crystal injection inlet is provided in the sealant 1.
The first glass substrate 3 is mounted on a table 4 in a vacuum container ‘C’ which is movable in a horizontal direction, and held by vacuum on the bottom surface of the first glass substrate 3 by a first plurality of vacuum holes 5.
Referring to FIG. 1B, the bottom surface of the second glass substrate 6 having a color filter array formed thereon is held by vacuum using a second plurality of vacuum holes 7. The vacuum container ‘C’ is closed and evacuated. The second glass substrate 7 is moved downward in a vertical direction until a gap between the first substrate 3 and second glass substrate 6 is 1 mm. The table 4 with supporting first glass substrate 3 thereon is moved in a horizontal direction to pre-align the first and second glass substrates 3 and 6 with respect to each other.
Referring to FIG. 1C, the second glass substrate 6 is moved downward until the second glass substrate 6 comes into contact with the liquid crystal 2 or the sealant 1. Referring to FIG. 1D, the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction to align the first and second glass substrates 3 and 6. Referring to FIG. 1E, the second glass substrate 6 is moved further down until the second glass substrate 6 bonds with the first glass substrate 3 through the sealant 1. The second glass substrate 6 is pressed down further until the gap between the second glass substrate 6 and the first glass substrate 3 becomes 5 m.
Referring to FIG. 1F, the pre-bonded first and second glass substrates 3 and 6 are taken out of the vacuum container ‘C’, and a UV ray is directed to the sealant to set the sealant 1, thereby completing the fabrication process.
However, the foregoing related art method for fabricating an LCD having the liquid crystal dropping method applied thereto has the following problems.
First, the sealant coating and liquid crystal dropping on the same substrate lead to require much fabrication time period before the two substrates are bonded.
Second, as the sealant is coated and the liquid crystal is dropped on the first substrate while the second substrate sits idle, there is an imbalance of a fabrication process time between the first and second substrates, resulting in an ineffective operation of the production line.
Third, because the sealant is coated and the liquid crystal is dropped on the first substrate, the first substrate can not be cleaned at an ultrasonic cleaner (USC). Therefore, as the sealant that will bond the two substrates should not be removed undesirable particles also cannot be removed which may cause defective contact of the sealant in the bonding.
Fourth, as the two substrates are aligned such that the either liquid crystal or the sealant comes into contact with the second substrate, the orientation film on the second substrate may become damaged, thereby causing poor picture quality. Further, if the upper and lower stages are not level, the first and second substrates may not fully contact each other and scratch the opposite substrate, or make the sealant uneven.
Fifth, aligning the two substrates by varying only a distance therebetween creates an inaccurate alignment of the two substrates.